1. Field of the Invention
The present invention relates to powder metallic salts of aliphatic monocarboxylic acids, for example, commercial stearic acid, and particularly to a modified powder form and method of manufacture.
2. Description of the Prior Art
Powder metallic salts of commercial stearic acid, commonly known as metallic stearates, which generally consists of 50% to 75% by weight stearic acid (octodecanoic acid), 25% to 50% by weight palmitic acid (hexadecanoic acid), and small amounts, i.e. generally less than 2% by weight, other C.sub.12 -C.sub.22 aliphatic saturated and unsaturated monocarboxylic acids, are used as additives in a variety of consumer products. For example, aluminum stearate is used as a defoamer for oil well drilling muds, a thickening agent for crayons, a gelling agent for greases and oils, and a suspension agent in paints and inks. Calcium stearate is used as a secondary stabilizer, mold release agent and lubricant in rigid PVC, a neutralizer of residual catalysts in polyethylene and polypropylene, and an anticaking agent in food applications. Magnesium stearate is used as a mold release agent in powders and tablets for cosmetic and pharmaceutical applications, a dispersant and anticaking agent for fire extinguisher powder mixtures, and a lubricant and processing aid in acrylonitrile-butadiene-styrene (ABS) polymers. Zinc stearate is used as a processing and lubricant aid for crystal and impact polystyrene, a dispersing agent in pigment blending, and a lubricant and mold release agent in polyethylene. Lead stearate is used as a stabilizer for PVC.
In many applications, a finely divided or small particle size, such as an average particle size in the range from 2 to 200 microns, is needed for the proper blending and functioning of the metallic stearate. In other applications, an average particle size up to 100 mesh (0.2 mm) can be used. Dry powder metallic stearates, after manufacture, are transported and handled in bulk form, for example, by tank car or truck or may be placed in bags which are then handled and transported to the user. At the user, the bulk metallic stearate, either from storage facilities or bags, is further handled and placed in hoppers to mixers and blenders. During this handling and transport, the fine powdery metallic stearate material is subject to producing dust which is hazardous. For example, metallic stearate dust, if ignited, can result in an explosion causing property damage and serious injury and death to personnel.
The prior art discloses adding 25% by weight mineral oil to the powder to suppress dust formation. However, such quantity of oil dilutes the powder and can often render the powder unsuitable for its intended purpose.